1. Field of the Invention
The present invention relates to a mobile network. More particularly, the present invention relates to a system and a method for performing a fast handoff in a mobile network using a mobile Stream Control Transmission Protocol (“mSCTP”).
2. Description of the Related Art
Currently, an Internet Protocol (“IP”) network, that is, an Internet network, and a wired interval in a cellular network has been simultaneously developed. Further, terminals operating within only a wired environment are also required to provide services while maintaining seamless connection in a fast wireless environment.
Because only a wireless environment is considered in the existing Internet environment, an IP address is allocated to a terminal only once. However, problems can arise where a connection is maintained through the allocated IP address and the terminal moves. This situation is exacerbated when a terminal using an IP address through which data is transmitted moves to another location and is also used in a wired interval of a mobile network environment where not only a voice communication function is available, but also a data communication function is added to the functionality of the terminal.
To solve the aforementioned problem, the Internet Engineering Task Force (“IETF”) has suggested a protocol called Mobile IP (“MIP”) for supporting the mobility of a terminal in a network layer. If the mobility of a terminal is supported in the network layer, a session can be maintained in a transport layer without recognizing the movement of the terminal. However, entities such as a home agent or a foreign agent should exist so as to support mobility in the network layer. The existence of such entities creates a problem in terms of overhead and inefficiency.
To address these concerns, mSCTP has been suggested as a new mobility support plan. The mSCTP is a protocol in which mobility is added to SCTP in an IETF working group. Although the SCTP was suggested as a transmission layer protocol for signal transmission, the SCTP has been currently specified as a conventional transport layer standard protocol for an IP network together with User Datagram Protocol (UDP) and Transmission Control Protocol (TCP). The SCTP is a connection-based transport protocol, similar to TCP, in which terminals located at two end-points establish a connection for communication performance. The connection is referred to as an association.
Further, the SCTP has multi-streaming and multi-homing characteristics. The multi-streaming divides data into a plurality of streams, and each of the divided streams is transmitted in accordance with the corresponding characteristic; multi-homing permits a host to have several EP addresses. Accordingly, TCP uses a combination of transmitter address, transmitter port number, recipient address and recipient port number to identify the connection, while SCTP identifies the association with transmitter IP address group, transmitter port number, recipient IP address group and recipient port number. Such multi-homing support can more flexibly cope with network defects, and provide a higher level of reliability than with an IP layer.
FIGS. 1A and 1B are network configuration views illustrating an operational process of mSCTP in a general mobile network.
Referring to FIGS. 1A and 1B, a Mobile Node (“MN”) 102 using mSCTP is located in an area 100 corresponding to subnet A that is within the jurisdictional area of Access Router (“AR”) #1 110. MN 102 uses IP address [1.1.1.1], and a Corresponding Node (“CN”) 130 with IP address [3.3.3.3], which is controlled by AR #3 140, recognizes the IP address of MN 102. Thereafter, the MN 102 may move to an overlay area where subnet A 100 and subnet B 150, controlled by AR #2 120, are overlapped with each other. Accordingly, the MN 102 adds a new IP address [2.2.2.2] (160) corresponding to subnet B 150. The MN 102 informs the CN 130 of the added IP address, the CN 130 then recognizes the newly added address. The MN 102 determines the presence of an addition of the new IP address through a process of comparing a preset critical value with reception signal intensity.
The MN 102 located in the overlay area uses the previous IP address, IP address [1.1.1.1], as the primary IP address, and the newly added IP address, IP address [2.2.2.2], as a secondary IP address. That is, the MN 102 using the mSCTP uses only the primary IP address to perform data transmission/reception, and the secondary IP address is used for data retransmission and backup.
When the MN 102 moves closer to the area of subnet B 150, the primary IP address is changed to [2.2.2.2] through comparison between a critical value and reception signal intensity. The MN 102 informs the CN 130 of the changed primary IP address (170), and the CN 130 recognizes the primary IP address of the MN 102. Further, after the MN 102 has completed the primary IP address change, IP address [1.1.1.1] is deleted (180) in the previous subnet (A), and CN 130 is informed of this completion.
FIG. 2 is a signal flow diagram illustrating an operational process in accordance with a handoff of MN in a conventional mobile network.
Referring to FIG. 2, MN 102 receives data from CN 130 (step 202). Thereafter, the MN 102 may move from a network in which data reception is currently possible to another network with a different subnet address. In this case, the MN 102 cannot receive data (204) transmitted from the CN 130 from a certain time point (step 206). The MN 102 completes a call setting through an Access Point (“AP”) and an L2 association of the newly moved network (step 208).
Thereafter, the MN 102 receives a Router Advertisement (“RA”) message periodically broadcasted from the AR 120 of the newly moved network, that is, New AR (“NAR”) 120 (step 210). As the RA message is received, the MN 102 recognizes that the MN 102 itself has moved to the network using another subnet (step 212). The RA message contains 64-bit prefix information of the NAR 120.
Thus, the MN 102 obtains a new IP address from the NAR 120, and transmits an AddresS CONFiguration Change (ADDIP ASCONF) signal to the CN 130 to inform of the newly obtained address. Further, the MN 102 transmits an ASCONF-SetPrimary signal to the CN 130 to inform that the primary IP address has been changed (Step 214). The CN 130 obtains the IP address of the MN 102, and adds a corresponding mSCTP association when receiving the AddresS CONFiguration Change (ADDIP ASCONF) signal. Further, the CN 130 transmits an ASCONF-ACK signal (step 216) informing MN 102 that the primary IP address has been changed when receiving the ASCONF-SetPrimary signal (step 214).
Having received the ASCONF-ACK signal, the MN 102 can receive data transmitted from the CN 130 for the first time (step 218). Meanwhile, if it is recognized that the previous AR and IP address are no longer required, the MN 102 transmits an ASCONF-DELETEIP signal to the CN 130 to delete the IP address (step 220). The CN 130 deletes the previous IP address from a corresponding SCTP association address list, and changes the primary IP address of the corresponding SCTP association into the IP address of a new subnet. The CN 130 then transmits an ASCONF-ACK signal to the MN 102 informing that the previous IP address has been deleted (step 222).
As described above, the MN 102 cannot receive data transmitted from the CN 130 during the period of step 206 to step 216 in accordance with a handoff of the MN 102.
FIG. 3 is a view illustrating a data processing delay time flow in accordance with an MN handoff in a conventional mobile network.
Referring to FIG. 3, the MN cannot receive data transmitted from the CN during the time of an L2 handoff corresponding to the AP change, a time when the RA message is received from the AR of the moved network, or a time when the primary IP address is changed. The L2 handoff delay time, for example, occurs for 100 msec to 1 sec, and the RA message reception delay time, for example, occurs for 1 to 10 sec. Thus, a delay time in accordance with a handoff of the MN using mSCTP occupies most of the time delay until the RA message is received.
Although the mSCTP supports handoff as described above, the MN using mSCTP cannot receive data due to the occurrence of delay time during handoff. Particularly, when there is a ping-pong handoff in which the MN changes different subnets at any time, the delay occurrence caused by the handoff creates a large overhead. Accordingly, there is an urgent need for a solution employing a fast handoff in a next-generation mobile communication system that aims at seamless connection in a fast radio environment.